Unhexnilium
Unhexnilium, Uhn, is the temporary name for element 160. NUCLEAR At least one set of theoretical values for half-lives and decay modes of Uhn have been constructed for neutron count up to N = 333(1). In order to understand what it reports about Uhn, it is valuable to review pp 15 and 18 in order to see patterns which extend over a range of elements. Ref. 1 predicts isotopes of Uhn in a band ranging from Uhn 433 to Uhn 468 which are to be expected for a neutron shell closure at N =308. As N increases, half-lives increase, decay mode switches from fission to alpha decay, and beta decay appears close to the upper end of the band. It also shows a band of isotopes from Uhn 469 to Uhn 480 which decay by alpha emission and have surprisingly long half-lives. It is not clear what influences create this zone: stabilization from Z = 164, stabilization from Z = 154, stabilization from N = 318, or something else. Beyond Uhn 480, the expected short-lived fissioning isotopes appear. What Ref. 1 can’t do is describe heavy isotopes of Uhu. At least two computations of the neutron \ dripline’s location up to Z = 175 exist(2),(3), which indicate that Uhn 571 is the heaviest possible Uhn isotope. Liquid-drop fission barrier for Uhn 571 is 2.4 MeV, which is almost enough to cause beta decay to predominate over fission. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(3),(4), 370(3), 318(5), and 308(1). The isotope Uhn 566 is expected to stabilize a band of isotopes from Uhn 571 down to at least Uhn 555 enough to cause them to beta-decay. (See “Formation” for additional significance of these nuclei.) Uhn 533 requires around 1 MeV of structural correction, and there is a possible doubly-magic nucleus at Upq 524. These may make possible some beta-decay chains from the neutron dripline to the band between Uhn 523 to Uhn 538. Since Ref. 1 does not clearly show a shell closure at N = 318, it should be noted that isotopes in the band Uhn 468 to Uhn 483 can be expected to decay by alpha emission if the shell closure is real. ATOMIC FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. It is likely that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uhn 555 to Uhn 571 to form in quantity during such a merger. It is also possible that beta-decay chains may reach from the neutron dripline to nuclides between Uhn 523 and Uhn 538. Lighter isotopes are unlikely to form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uhn 434 to Uhn 483 band. Quantities produced by this method are very small. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 3. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 4. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-15-19)